California Department of Transportation

MAP- 21 National Highway System

On October 1, 2012, Section 1104 of MAP-21 expanded the National Highway System (NHS) to include all existing Principal Arterials (i.e. Functional Classifications 1,2 and 3) to the NHS.

NHS Summary

Per MAP-21, the NHS is composed of approximately 160,000 miles of rural and urban roads nationwide serving major population centers, international border crossings, intermodal transportation facilities, and major travel destinations. The NHS includes the following:

  • The Interstate System.
  • Principal arterials (including those not previously designated as part of the NHS) and border crossings on those routes.
  • Intermodal connectors -- highways that provide motor vehicle access between the NHS and major intermodal transportation facilities
  • STRAHNET (Strategic Highway Network) -- the network of highways important to U.S. strategic defense
  • STRAHNET connectors to major military installations.

MAP-21 Legislation

FHWA q & a's

Federal Highway Administration questions and answers regarding the NHS following the implementation of MAP-21:

NHS Database:


To view a map of the NHS, go to Caltrans Earth, then on the left column click "Highways", then "Map-21 NHS.".


  • For further information on how to add or remove a route from the NHS, CLICK HERE
  • For a flowchart summary of the process, CLICK HERE.


Page Updated on September 3, 2014